Where does Leonard imagine himself to be?

Leonard Mead is the protagonist in Ray Bradbury's short story "The Pedestrian." Every evening Leonard Mead leaves his house and goes out for a walk. This seemingly innocuous activity is his favorite thing to do.

. . . to put your feet upon that buckling concrete walk, to step over grassy seams and make your way, hands in pockets, through the silences, that was what Mr. Leonard Mead most dearly loved to do.

As he walks past each home, he wonders what each person in that house is watching on television. Mead is utterly alone on his walks. Nobody does this kind of activity any more, and that is why he is ultimately picked up by a police car and brought to a psychiatric ward. The world he lives in thinks going outside and not watching television is akin to insanity. Mead loves it, and he loves it because of the solitude and silence. It's so lonely and quiet that Mead is capable of imagining himself in the middle of nowhere. He specifically imagines himself on a windless desert floor.

If he closed his eyes and stood very still, frozen, he could imagine himself upon the center of a plain, a wintry, windless Arizona desert with no house in a thousand miles, and only dry river beds, the streets, for company.